This Interagency Agreement provides support for the Protein Data Bank (PDB), a database resource for studying biological macromolecules. The PDB archive is the single worldwide repository of information about the 3D structures of large biological molecules, including proteins and nucleic acids. The database contains information about experimentally-determined structures of proteins, nucleic acids, and complex assemblies. The U.S. RCSB PDB is a member of the Worldwide Protein Data Bank (wwPDB), which consists of organizations that act as deposition, data processing and data distribution centers for PDB data. The mission of the wwPDB is to maintain a single Protein Data Bank Archive of macromolecular structural data that is freely and publicly available to the global community. PDB data is curated and annotated according to agreed upon standards. A variety of software tools and information analysis resources are also provided. Users can access the information system through a web site to perform simple and advanced searches based on annotations relating to sequence, structure and function. These molecules are visualized, downloaded, and analyzed by users who range from students to specialized scientists. The RCSB PDB website at www.pdb.org is accessed by about 140,000 unique visitors per month from nearly 140 different countries. Around 500 GigaBytes of data are transferred each month. Data are accessed via the website, ftp server (supporting ftp and rsync access), Web Services and RSS feeds.